The present invention relates generally to a valve device and, more particularly, to a valve device which is adapted to an On-Board Diagnostics-II (OBD-II) system for diagnosing leakage or faults in a fuel system or fuel vapor purge system for vehicles.
Recently, vehicles exported to North America and domestic vehicles are usually equipped with a leakage and fault diagnosing system, which is provided in a fuel tank and a fuel or fuel vapor prevention device, thus allowing a driver to immediately be made aware of a fault.
A vehicle equipped with a canister close valve is provided with a fuel-system protecting structure, which is constructed so that a safety pipe is mounted on a pipeline coupling a canister to the canister close valve, thus preventing a fuel system from being broken or damaged by fuel vapor.
As well known to those skilled in the art, research on all aspects of exhaust-gas purging by a vehicle has been conducted. However, since harmful elements are produced by various causes, it is not easy to purge all harmful elements produced by different causes. Meanwhile, the main element of fuel vapor contained in the harmful exhaust gas is hydrocarbon (HC). Hydrocarbons are harmful to the respiratory organs and eyes. Further, hydrocarbons combine with nitrous oxide, thus forming photochemical smog.
For these reasons, the U.S. Environmental Protection Agency and the California Air Resources Board require the prevention of fuel vapor from being discharged to the atmosphere when the amount of fuel vapor leaking from a pipe extending from a fuel tank to an intake manifold is measured and the measured amount exceeds a permissible amount. Further, they propose a diagnostic device or a leakage diagnosis method.
Meanwhile, various systems for suppressing fuel vapor have been proposed. Among them, a charcoal canister method using activated charcoal is executed as follows. That is, hydrocarbons contained in fuel vapor which is evaporated in a fuel tank 1 are collected in a canister 4 which stores activated charcoal therein. When a canister close valve (CCV) 5 is opened, the collected hydrocarbons are discharged from the canister 4 by external air flowing through the canister close valve 5. The hydrocarbons pass through a purge control valve 7, a surge tank 6, and an intake pipe 12, and are supplied to a combustion chamber to be burned in the combustion chamber.
Further, in such a fuel vapor suppressing system, fine holes may be formed in an evaporation-gas line, and evaporation gas may leak from the evaporation-gas line. In this case, the leaking evaporation gas causes atmospheric pollution. Thus, it is determined that the evaporation-gas suppressing system is out of order. At this time, a fault detection lamp is turned on, thus informing a driver of the fault. Such an operation is called an operation of monitoring the fuel vapor suppressing system.
In this case, the canister close valve 5 closes the fuel system in a monitoring area. When the hardware of the canister close valve 5 is stuck closed, it may not function. This event is detected by an electronic control unit (not shown), thus stopping a canister purge operation, therefore preventing damage due to the excessive reduction in pressure of the fuel system.
Further, even if the canister close valve 5 develops such an error but a user does not take appropriate measures quickly, the pressure of the closed fuel system increases due to fuel vapor. When fuel temperature is relatively high, especially as in the summer, and pressure is not appropriately discharged, the pressure of the fuel system is continuously increased by fuel vapor, and thus the fuel tank 1, the canister 4, and a vapor separator may break.